1. Field of the Invention
The present invention relates to a nitride-based semiconductor light emitting diode (LED) which enhances current spreading efficiency by improving the structure of electrodes and electrode pads, thereby implementing a low driving voltage.
2. Description of the Related Art
In general, a nitride-based semiconductor is Group III-V semiconductor crystal having a compositional formula of AlxInyGa(1-x-y)N (herein, 0≦x≦1, 0≦y≦1, and 0≦x+y≦1) and is widely used for LEDs which can emit short-wavelength light (ultraviolet or green light), or particularly blue light.
Meanwhile, the nitride-based semiconductor LED is manufactured using an insulating substrate such as a sapphire substrate or SiC substrate which satisfies a lattice matching condition for crystal growth. Therefore, the nitride-based semiconductor LED has a planar structure that two electrodes connected to first and second conductive-type nitride semiconductor layers are arranged horizontally with the top surface of a light emission structure.
Recently, there is a demand for high luminance, in order to use the nitride-based semiconductor LED having a planar structure as a lighting source. To implement high luminance, a nitride-based semiconductor LED is being manufactured, in which a current can be uniformly spread to enhance light emission efficiency.
However, in the nitride-based semiconductor LED having a planar structure, a current flow is not uniformly distributed in the entire light emitting region, compared with a nitride-based semiconductor LED having a vertical structure that two electrodes are disposed on the top and bottom surfaces of a light emission structure, respectively. Therefore, an effective area used for light emission is not large, so that light emission efficiency is degraded.
Now, the problems of the conventional nitride-based semiconductor LED having a planar structure will be described in detail with reference to FIGS. 1 and 2.
FIG. 1 is a plan view of the conventional nitride-based semiconductor LED. FIG. 2 is a cross-sectional view taken along line II-II′ of FIG. 1.
As shown in FIGS. 1 and 2, the conventional nitride-based semiconductor LED having a planar structure includes a buffer layer 110, a first conductive-type nitride semiconductor layer 120, a GaN/InGaN active layer 130 with a multi-quantum well structure, and a second conductive-type nitride semiconductor layer 140, which are sequentially formed on a sapphire substrate 100. The second conductive-type nitride semiconductor layer 140 and the active layer 130 are partially removed by mesa etching such that the top surface of the first conductive-type semiconductor layer 120 is partially exposed.
On the exposed first conductive-type nitride semiconductor layer 120, a plurality of first conductive-type electrode pads 160a, a plurality of first conductive-type electrodes 160, and a first conductive-type connection electrode 160b are formed. The first conductive-type connection electrode 160b extends from the first conductive-type electrode pads 160a so as to connect the first conductive-type electrodes 160.
On the second conductive-type nitride semiconductor layer 140, a transparent electrode 150 composed of ITO (Indium Tin Oxide) is formed. On the transparent electrode 150, a plurality of second conductive-type electrode pads 170a and a second conductive-type connection electrode 170b for connecting the second conductive-type electrode pads 170a are formed.
On the transparent electrode 150, a plurality of second conductive-type electrodes 170 are formed to extend from the plurality of second conductive-type electrode pads 170a and the second conductive-type connection electrode 170b in one direction. The conventional nitride-based semiconductor LED has a finger structure that the second conductive-type electrodes 170 are engaged with the first conductive-type electrodes 160, respectively. Therefore, in the conventional nitride-based semiconductor LED, the second conductive-type electrodes 170 and the first conductive-type electrodes 160 are spaced at a uniform distance from each other on the entire surface of the LED such that a current flow can be uniformly spread in the entire light emitting region of the LED.
In the conventional nitride-based semiconductor LED, the first and second conductive-type electrode pads 160a and 170a are connected to the respective electrodes through the first and second conductive-type connection electrodes 160b and 170b. 
However, when the first and second conductive-type electrode pads 160a and 170a or the first and second conductive-type electrodes 160 and 170 are connected to each other through the first and second conductive-type connection electrodes 160b and 170b, respectively, an effective area used for light emission is reduced as much as the regions where the first and second conductive-type connection electrodes 160b and 170b are formed, with respect to the entire light emitting area.
Further, the first conductive-type electrode pads 160a and the second conductive-type electrode pads 170a are respectively formed on different sides, that is, on sides facing each other.
However, when the first conductive-type electrode pads 160a and the second conductive-type electrode pads are respectively formed on different sides facing each other, an effective area used for light emission is partially reduced as much as the regions where the first and second conductive-type electrode pads 160a and 170a are formed, with respect to the entire light emitting area. Then, the overall light emission efficiency decreases.